Extensive effort has been devoted to development of aircraft that are capable of taking off, hovering, and landing like a helicopter—that is, in rotary wing flight mode—and that are also capable of high speed cruise—that is, fixed wing flight mode. A recent example of such an aircraft is the canard rotor/wing (“CR/W”) aircraft. An exemplary CR/W aircraft is discussed in U.S. Pat. No. 5,454,530, the entire contents of which are hereby incorporated by reference.
A CR/W aircraft is propelled by a turbofan engine and a reaction drive system. During rotary wing flight, the turbofan engine's exhaust powers the rotor system through ducts to nozzles near the rotor tips. During conversion to fixed wing flight, the turbofan engine's exhaust is redirected from the reaction drive rotor tip nozzles aft to conventional nozzles. During this transition, residual exhaust continues to rotate the rotor, and a canard and horizontal tail provide lift for remaining aloft.
In some CR/W aircraft, the reaction drive rotor tip nozzles may include ducts that protrude beyond the airfoil boundary. In such an arrangement, the protruding, open ducts may increase aerodynamic drag during fixed wing flight. Further, gas flow is not choked during the transition from rotary wing flight to fixed wing flight. That is, nozzle pressure ratio is not optimized, thereby resulting in loss of flow specific thrust.
In other arrangements, the reaction drive rotor tip nozzles may include ducts that do not protrude beyond the airfoil boundary, and a pair of hinged nozzle flap doors may be incorporated into the airfoil boundary. Exemplary nozzle flap doors are discussed in U.S. Pat. No. 5,788,181, the entire contents of which are hereby incorporated by reference. The nozzle flap doors are fully opened during rotary wing flight and fully shut during fixed wing flight. Such an arrangement reduces aerodynamic drag during fixed wing flight. However, this arrangement does not overcome loss of specific flow thrust.
The foregoing examples of related art and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.